"I don't actually recommend trying to go there and get some for yourself - it takes a long time, it's somewhat uncomfortable, you're not guaranteed results at the end of it, and if something goes wrong with your interworld transport you may end up stuck in a dead universe - but my Sense has been awfully handy so far. I can tell what spells are on me and what they do, I can tell roughly what sorts of magical capabilities a person has, that sort of thing."